Apparatus and process for undersea mining of mineral bearing sand and gravel

ABSTRACT

A process and mobile apparatus for the undersea mining of sand and gravel deposits containing gold particles and associated heavy minerals such as platinum, magnetite, etc., includes an excavating device which continuously excavates the sand and gravel material. Conveyor means receive the excavated sand and gravel and conveys the material to a discharge point which is located a predetermined distance above and a predetermined distance upstream from a screen type collection device. The predetermined difference in elevation and the downstream spacing between the collection device and the discharge point is so related to the ambient ocean current adjacent the ocean floor that separation of the sand and gravel discharged from the discharge point takes place as a result of the action of gravity and the subsurface ambient current acting on the material. The gold and associated metal particles (platinum, magnetite, etc.) and sand and gravel particles which are slightly coarser than the gold particles will be moved downstream by the ambient ocean current as the material falls and will be received by the collection device, while the sand particles will be carried downstream beyond the collection device, and the more coarse materials will fall upstream with respect to the collection device.

United States Patent 1 1 Lindelof [54] APPARATUS AND PROCESS F ORUNDERSEA MINING OF MINERAL BEARING SAND AND GRAVEL [75] Inventor:Leonard A. Lindelof, Minneapolis,

Minn.

[73] Assignee: QVA Corporation, Minneapolis,

Minn.

[22] Filed: Nov. 18, 1971 [2]] Appl. No.: 199,986

Primary ExaminerErnest R. Purser Att0rney-George F. Williamson et a1.

1 1 May 8,1973

[ 57] ABSTRACT A process and mobile apparatus for the undersea mining ofsand and gravel deposits containing gold particles and associated heavyminerals such as platinum, magnetite, etc., includes an excavatingdevice which continuously excavates the sand and gravel material.Conveyor means receive the excavated sand and gravel and conveys thematerial to a discharge point which is located a predetermined distanceabove and a predetermined distance upstream from a screen typecollection device. The predetermined difference in elevation and thedownstream spacing between the collection device and the discharge pointis so related to the ambient ocean current adjacent the ocean floor thatseparation of the sand and gravel discharged from the discharge pointtakes place as a result of the action of gravity and the subsurfaceambient current acting on the material. The gold and associated metalparticles (platinum, magnetite, etc.) and sand and gravel particleswhich are slightly coarser than the gold particles will be moveddownstream by the ambient ocean current as the material falls and willbe received by the collection device, while the sand particles will becarried downstream beyond the collection device, and the more coarsematerials will fall upstream with respect to the collection device.

5 Claims, 3 Drawing Figures PATENTEU MAY 8 1973 INVENTOR; Leonard A.Lindelof Wan APPARATUS AND PROCESS FOR UNDERSEA MINING OF MINERALBEARING SAND AND GRAVEL SUMMARY OF THE INVENTION It is generally knownthat gold and associated heavy minerals are widely distributed in thesand and gravel sediments of submerged beaches and drowned river valleysof the continental shelf areas. Local concentrations of gold have beenidentified in surface sediments in the continental shelf off southernOregon, and there is reason to believe that such concentrations existoff the shores of all five continents.

Although the presence of the gold particles throughout the sand andgravel sediments of the continental shelf areas is generally known,there are no known economic processes or methods of mining the sand andgravel deposits to economically remove the gold particles therefrom.Therefore, if it is assumed that gold is valued at 35 dollars an ounce,and it is further assumed that the recoverable concentration of goldparticles in the sand and gravel deposits is approximately 25 cents peryard, then extremely large volumes of sand and gravel would have to beprocessed in order to justify mining these undersea deposits.

It is therefore a general object of this invention to provide apparatusand process for the undersea mining of sand and gravel depositscontaining gold which may be economically accomplished even if, forexample, the concentration of gold particles is no greater than 25 centsper yard (based on gold valued at 35 dollars an ounce). Generallyspeaking, the present process and apparatus contemplates concentratingor beneficiating the gold bearing sand and gravel deposits by using theaction of gravity and the ambient subsurface ocean current to produce aninitial separation of the gold particles from the sand and graveldeposits.

In this regard, the sand and gravel deposits containing the goldparticles is continuously excavated by an undersea mobile excavatingdevice and the excavated material is moved to a predetermined height bysuitable conveyor means. The excavated sand and gravel deposits iscontinuously discharged at a predetermined height directly into theambient ocean current. A collection device, preferably a reciprocatingscreen type, is positioned below and downstream from the dischargepoint. The difference in elevation and the downstream spacing betweenthe discharge point of the sand and gravel and the reciprocating screencollection device is so related to the magnitude of the ambient currentas to cause the gold particles and the coarser sand and fine gravelunder the influence of gravity and the ambient current to falldownstream upon the reciprocating screen receptacle. Although the goldparticles are of comparable weight to the coarser sand and fine gravelparticles, the gold particles are smaller and the reciprocating screenwill produce a further separation.

The fine sand particles will be moved downstream beyond thereciprocating screen receptacle under the influence of the ambientcurrent and the action of gravity while the heavier larger particleswill fall upstream upon the ocean floor with respect to the collectiondevice. Thus the use of the ambient current as a means of initiallyseparating gold particles from sand and gravel deposits makes possiblethe economic mining of these deposits. These and other objects andadvantages of this invention will more fully appear from.

the following description made in connection with the accompanyingdrawings wherein like reference characters refer to the same or similarparts throughout the several views.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS FIG. I is adiagrammatic perspective view of the apparatus used in carrying out thenovel process;

FIG. 2 is a diagrammatic elevational view of the apparatus showing apatterned separation of the gold bearing sand and gravel under theinfluence of gravity and the subsurface ambient current; and

FIG. 3 is a plan view of the reciprocating screen used in conjunctionwith the collection device.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings andmore specifically to FIG. I, it will be seen that one embodiment of thenovel underwater mining apparatus, designated generally by the referencenumeral 10, is there shown. This apparatus is adapted to be controlledby a large ocean going surface craft 1 1, preferably an ocean goingbarge which is also capable of receiving the refined or beneficiatedgold bearing deposits. In this regard, the underwater mining apparatus,in the embodiment shown, is adapted to be remotely controlled from thesurface craft and a conduit 12 interconnects the surface craft II withthe underwater mining apparatus. The conduit not only provides a passagefor the refined gold bearing sand and gravel deposits, but also hasassociated therewith suitable electrical control cables to permit remotecontrol of the undersea mining apparatus.

The mining apparatus I0 is adapted for continuous mining of the sand andgravel deposits which constitute the ocean floor and which contain goldparticles. In the embodiment shown, apparatus 10 includes aselfpropelled crawler type bucket wheel excavator which in generalconstruction may resemble the commercially available bucket wheelexcavators. This excavator includes a revolvable bucket wheel 14 havinga plurality of buckets or scoops which are circumferentially arranged sothat as the bucket wheel is revolved, the sand and gravel deposits willbe excavated and will be directed to an endless conveyor 18. Therevolvable bucket wheel is mounted at the outer end of an elongate boom15 which is shiftably connected at its inner end to the body I6 of theexcavator. The body 16 is mounted for traversing movement along the seafloor by suitable surface engaging crawler assemblies I7.

The endless conveyor I8 conveys the sand and gravel deposits excavatedby the revolvable bucket wheel 14 to a suitable guide type hopper device19 positioned. adjacent the discharge end of the endless conveyor 18.The sand and gravel material are then conveyed to an elevator typeconveyor 20 to a predetermined height where the material is discharged.Thus the elevator type conveyor 20 has one end portion thereof whichreceives the sand and gravel material from the endless conveyor Wand hasa discharge end or discharge point 21 from which the sand and gravelmaterial is discharged. The elevator conveyor is vertically adjustableso that the vertical spacing between the point of discharge of theconveyor and a collector device 22 may be variously adjusted.

It is also desirable to properly orient the sand and gravel materialdischarged from the conveyor 20 so that this material will be directedin its downward descent from a discharge point which is disposed in avertical plane arranged substantially normal to the direction of thesubsurface ambient ocean current. To this end, a substantially flatinclined deflector device 24 is provided and is positioned slightlybelow and adjacent the discharge end 21 of the conveyor 20 to receivethe sand and gravel material discharged therefrom. The deflector device24 is inclined downwardly in the direction of the subsurface ambientcurrent and may be provided with an upstanding flange 25 afflxed to theperipheral edges thereof. Suitable direction control vanes 26 may beaffixed to the upper surface of the deflector device and these vanes maybe preferably arranged so that they diverge towards the discharge edge24a thereof. It will be noted that the discharge edge 24a of thedeflector device is substantially Straight and disposed in a verticalplane arranged substantially normal to the subsurface ambient oceancurrent. Since the discharge edge or point 24a of the deflector device24 is disposed in a vertical plane arranged substantially normal to theambient current, the

downstream spacing between the discharge point 24a and the collectiondevice may be more accurately determined. It is pointed out that thedeflector device 24 is also vertically adjustable with the conveyor 20so that the vertical spacing between the discharge point 24a and thecollector device may be readily adjusted.

The collection device 22 is provided with a sectional reciprocatingscreen 23 at its upper surface which is operable to produce furtherseparation of the gold particles from the sand and gravel particles. Thesectional screen as shown includes a plurality of sections arranged sideby side including screen section 23a, screen section 23b, and screensection 23c. It will be noted that the mesh size of screen section 23ais larger than the mesh size of screen section 23b, and that the meshsize of screen section 23b is larger than the mesh size of screensection 23c. it is apparent that additional screen sections could alsobe provided. The sectional reciprocating screen 23 reciprocates in thedirection of the arrows so that the coarser material which will not passthrough the screen section will be progressively conveyed along anddischarged from the screen section. For example, the gold particles willpass through the openings in the screen section 23a while the gravel andcoarser sand will be conveyed longitudinally along the screen section23a and will be discharged therefrom.

These screen sections are so arranged that the smaller screen size islocated further downstream from the larger screen size. Suitable arrowsindicate the direction of the subsurface current. Thus the heavier andlarger particles will fall upon the larger mesh screen section.

It will be noted that the conduit 12 is interconnected to the collectordevice 22, and, although not shown, a suitable pump will be provided forpumping water entrained beneficiated gold bearing sand and gravelupwardly to the surface craft 11. it is also pointed out that in someinstances, further refinement below the surface of the water of thebeneflciated gold bearing sand and gravel may be accomplished withadditional known mechanical separating means. However, for the purposesof this invention, the beneficiated gold bearing sand and graveldeposits are illustrated as being pumped to the surface craft after ithas been collected in the collector device 22.

One of the natural characteristics of the ocean is the essentialcondition which permits economic operation of the present process andapparatus. This characteristic of the ocean is ambient subsurfacecurrent and it is necessary to determine the direction of the current,as well as the magnitude of the current for optimum results with respectto the present process and apparatus.

Generally speaking, the sand and gravel deposits constituting the oceanfloor may be mined in any direction but it is essential that theexcavated gold bearing sand and gravel deposits be discharged so thatthe material is influenced by the ambient current as material falls byaction of gravity towards the collection device. It will be seen thatthe collection device is positioned at a substantially lower level thanthe discharge point of the conveyor 20 and is also positionedsubstantially downstream from the discharge point. The vertical spacingand downstream spacing between the discharge point and the collectiondevice will vary according to the magnitude of the ambient current. Ithas been found that the subsurface ambient current adjacent the oceanfloor varies within the range of A knot to approximately 4 knots.Although the vertical spacing between the discharge point 24a of thedeflector and the collection device will vary over a relatively largerange, experimental evidence indicates that a desirable workable rangefor this vertical spacing is approximately 10 to 40 feet. It is alsopointed out that the discharge point 24a would be spaced verticallyabove the ocean floor F a distance of 25 to 100 feet.

It has been found that the gold particles which are disseminatedthroughout the sand and gravel deposits of the Pacific continental shelfarea, especially off the North American coast vary in size fromparticles which are of a size that will pass through a 10 mesh screen,but not a 20 mesh screen (plus 20) and those that are of a size thatwill pass through a 100 mesh screen (minus 100). It is thought thatprobably the greatest amount of recoverable gold and associated mineralparticles occur within the range of sizes between minus 40 and plus 100and smaller. The weight of these individual particles has been generallycalculated to be approximately 1.0072 grams for the minus 10, plus 20particles, 0.003 grams for the minus 20, plus 40 particles, and 0.0005grams for the minus 40, plus 100 particles.

The average descent time of gold particles in water, as well as otherparticles, can also be determined and this information must be known inorder to properly interrelate the discharge point of the conveyor 20with respect to the collection device 22. Gold particles of a minus 10,plus 20 size have an average descent time of approximately 3.52 secondsin a 35 inch vertical column of water. Similarly, gold particles of aminus seconds in the same column of water. Gravel, on the other hand, ofa plus size has an average descent time of approximately 4.13 secondswhile the average descent time for sand depends upon the size of thesand particles. In this regard, sand ofa minus 10, plus size has anaverage descent time of approximately 6.20 seconds, a minus 20, plus 40size sand particles has an average descent time of approximately 11.20seconds, and sand particles of a minus 40, plus 100 size has an averagedescent time of approximately 23.20 seconds.'

The sand and gravel descent times were also based on a vertical columnof water approximately 35 inches in height.

It has also been determined that the particular configuration of thegold particles affects the descent characteristics of the particle inwater. In this regard, the heavier, bulky particles without beinginfluenced by any ambient current will fall directly down without anyspinning motion, while the flatter shaped particles while descendingstraight down at a slightly lower rate tend to spin rapidly about avertical axis. In every instance the gold particles descend faster thansand or gravel particles of the same approximate size. In a given screensection, smaller bulky shaped (fast descent) particles will be collectedalong with the larger particles for which the screen is sized.

It has been determined that the coarser sand and fine gravel of theocean floor deposits will have the same general rate of descent as therate of descent of the gold particles found in these deposits. Thus,when the discharge point of the elevator conveyor is arranged in itspredetermined relation with respect to the collector device, the goldparticles within the range of minus 10,

plus 20 to minus 100 (the size of particles normally exprogressivelysmaller. With this arrangement, the

heavier but smaller gold particles will fall through the openings in thescreen section 23a while the plus 10 gravel particles will be conveyedas tailings from the section. The progressively smaller screen sizeswill permit the same separation with respect to those sand, gravel andgold particles carried further downstream by the ambient current and theaction of gravity.

When the direction of the ambient ocean current as well as the magnitudethereof is determined, the verti cal spacing between the discharge pointfor the ex cavated sand and gravel deposits and the collection devicemay be determined and the downstream spacing between the discharge pointand the collection device may also be determined. It will be seen thatthe heavier larger particles will obviously be less influenced by theambient current and will fall upstream with respect to the collectiondevice. The gold particles and coarser sand and fine gravel will beinfluenced by the subsurface ambient current and will be moveddownstreamfrom the point of discharge and fall upon the collectiondevice 22. The ambient current will cause the lighter weight particlesto be carried downstream beyond the collection device. Thus, since thecurrent is continuously present, it will be seen that it is merelynecessary to adjust the vertical spacing and the downstream spacingbetween the discharge point and the collection device, depending uponthe magnitude of the current.

Test experience indicates that the present process permits a highpercentage recovery of the gold particles in the sand and graveldeposits. It is thought that the percentage of gold recovery from thesand and gravel deposits should exceed 92 percent and is thought to beas high as 95 percent recovery. it has also been found that that portionor cut of the sand and gravel deposits that would be directed to thecollection device by the action of gravity and the ambient subsurfacecurrent is approximately 25 percent of the entire material constitutinga yard of material excavated. Therefore, assuming that the quantity ofgold particles in each yard of sand and gravel deposits is approximately$0.25 per yard, then based on the test evidence of expected recovery(that is, a 90 percent of the gold available in a yard of material) thenapproximately $0.225 worth of gold would be recovered along with 0.250yards of sand and gravel. The ore would be beneficiated to 22.5cents/0.250 yards 90 cents/yard. This calculated beneficiated value, 90cents/yard, results solely from the gravity-current separation and wouldtherefore be the calculated value of the ore falling upon the screen.

As pointed out above, the present beneficiation (by ambient currentseparation) of the gold bearing sand and gravel deposits has been basedon a recovery of 90 percent of gold bearing particles from each yard ofthe deposit process. Because of the classifying effect of the ambientcurrent the material landing on the screen can be beneficiated by anadditional 90 percent by the screening action. Therefore, if each yardof sand and gravel deposit contains gold particles having a value of 25cents (based on a 35 dollar per ounce value of gold) then it is thoughtthat using the present process, each yard of the beneficiated materialwould have a value of $9.00 (90 I01 yard). It is also pointed out thatpreliminary sampling would be run to show the particle sizeclassification of not only gold, but the sand and gravel deposits. Assoon as this information is made known, the economics of the goldseparation with respect to any given sand and gravel deposit could bereadily estimated. 1

it is thought that the present apparatus should be capable of processingapproximately 10,000 yards of ore (mineral bearing sand and graveldeposits) per hour. An example of the equipment having the capability toaccomplish this operation would, for example, typically require arevolvable bucket wheel ll l having a diameter of 50 feet and-mounted onan elongate boom 15, having a length dimension of approximately feet.The boom 15 would be swingably mounted on the body 16 so that its arc ofswinging movement would permit the excavation of a trench approximately(142) feet wide. The forward velocity of the apparatus would beapproximately (6.35) inches per minute. The endless conveyor 18 and theconveyor 20 would typically be approximately (20) feet wide and eachwould carry excavated material thereon having a depth dimension ofapproximately (22.5) inches at a velocity of approximately (2) feet persecond. The distributor or deflector 24 will be of a size to distributethe material over a length corresponding to the length (preferably 60feet) of the sectional screen of the collection device. Again, thedischarge point 24a under normal conditions would preferably be spacedfrom about (25) feet to (100) feet above the surrounding ocean floor.

It will be seen that the downstream spacing of the leading edge of thesectional screen 23 would be dependent on the velocity of the ambientsubsurface current and on the characteristics of the ore. Assuming thesubsurface ambient current to be approximately 1 knot (1.69 feet persecond), the collection device and leading edge of the sectional screencould be typically located approximately feet below and approximately 25feet to 80 feet downstream with respect to the discharge point 24a ofthe distributor. The width dimension of the sectional screen assembly 23would be approximately (40) feet and the width dimension would beoriented in the direction of the ambient current. The sectional screenassembly would also preferably be approximately (60) feet long and wouldreciprocate in a direction disposed substantially normal to thedirection of the ambient subsurface current.

As pointed out above, the material excavated with this apparatus wouldbe approximately 10,000 yards of material per hour and approximately(2,500) yards per hour of this material would land on the reciprocatingscreen. Approximately (250) yards per hour of this material would passthrough the screen and approximately (2,250) yards per hour of thematerial would pass over the end of the screen as tailings. It ispointed out that the reciprocating screen of a size and having thegeneral features described hereinabove would be capable of this capacityunder normal operating conditions. If material is conveyed along thescreen at a velocity of (2) feet per second, the average depth ofmaterial on the sectional screen 23 would be approximately (2) inches.It will be appreciated that the capacities and sizes of the componentsof the above described apparatus are merely illustrative of theapparatus that would be employed to process approximately l0,000 yardsof ore per hour.

It will be further appreciated from the aforementioned description thatthe primary energy which is used to accomplish the separation of goldand associated metals from the sand and gravel deposits is thesubsurface ambient ocean current. The quantum of energy provided by theambient ocean current is very substantial. This quantity of energy canbe more readily envisioned if it is contemplated that ambient currenthas a velocity of approximately 1 knot and the material to bebeneficiated is dropped from a height of approxi mately l5) feet and isdischarged from a distributor so that the material will fall on a screenhaving a length of approximately (60) feet. By way of contrast, if thesame amount of water were supplied in a land based operation and waspumped against only a 10 foot head without allowing for any losseswhatsoever, then well over (1,000) horsepower would be required.However, in actual practice, it is thought that approximately Ihorsepower per hour yard per of ore would be required to provide thenecessary washing, separation and classifying action obtained bydischarging the ore into the ocean current.

From the foregoing description, it will be seen that l have providednovel process and apparatus for economically mining the sand and graveldeposits that constitute the ocean floor. It will be seen that thepresent process contemplates the use of the ambient ocean current alongwith the action of gravity to provide a means of beneficiating the goldbearing sand and gravel deposits. Thus in carrying out the process on aneconomical basis, it is merely necessary to sample the deposits to beprocessed to determine the textural characteristics of the deposit andthen to determine the magnitude and direction of the ambient current toproperly orient the discharge point with respect to the collectionpoint. The present process and apparatus is capable of extremely highvolume operation and thus renders possible the economic recovery of goldparticles from sand and gravel where the amount of gold in each yard ofdeposit is extremely small. Thus it will be seen that l have providedanovel process and apparatus of a type never before contemplated for theeconomic undersea mining of gold bearing sand and gravel deposits.

What is claimed is: 1. A process for high volume undersea mining of goldbearing sand and gravel deposits, comprising excavating undersea sandand gravel deposits containing gold particles,

conveying the excavated gold bearing sand and gravel deposits to adischarge point located adjacent the ocean floor,

positioning a collection medium at a predetermined distance below thedischarge point, and at a predetermined distance downstream from thedischarge point with respect to the ambient subsurface current adjacentthe ocean floor, discharging the excavated gold bearing sand and gravelmaterial from the discharge point and allowing the material to fall byaction of gravity, the predetermined downstream spacing and thepredetermined vertical spacing between the collection medium and thedischarge point being so related to the magnitude of the ambient oceancurrent adjacent the ocean floor so that the coarse sand and finegravel, and the gold particles will move downwardly and downstream underthe influence of gravity and the ocean ambient current and will bereceived by the collection medium, while the finer sand deposits will becarried downstream beyond the collecting medium, and the heavierparticles will fall upstream from the collection medium.

2. The process as defined in claim 1 and screening the material receivedby the collection medium whereby the smaller gold particles will besepararated from the coarser sand and fine gravel particles.

3. The process as defined in claim 1 wherein said gold bearing sand andgravel deposits is continuously excavated and is continuously conveyedto the discharge point to be continuously discharged therefrom.

4. Apparatus for undersea mining of sand and gravel deposits containinggold particles comprising an excavating device adapted to be moved alongthe ocean floor for continuously excavating gold bearing sand and graveldeposits, the conveying device having a receiving portion for receivingexcavated sand and gravel material, and having a discharge portion,

a collection device having an upper portion posigravel particles will bemoved downwardly and tioned a predetermined distance be o Sai downstreamunder the influence of gravity and the discharge portion of the conveyordevice, and being disposed a predetermined distance downstream from thedischarge portion of the conveyor device with respect to the subsurfaceambient ocean current, the predetermined from the collection devicedownstream spacing and the predetermined dif- 5 Th t d l 4 h ference inheight between the collection device appafa i as 6 me P c w erem and thedischarge portion of the conveyor being 10 collection device lncludes areciprocating screen at its related to the magnitude of the ambientocean curupper Porno and the gold particles and rent adjacent the oceanfloor so that the gold par'tithe coarser sand and gram Pamcles cles andthe accompanying coarse sand and fine ambient subsurface ocean currentand received by the collection device, while the finer sand particleswill be carried downstream beyond the collection device, and the heavierparticles will fall upstream

1. A process for high volume undersea mining of gold bearing sand andgravel deposits, comprising excavating undersea sand and gravel depositscontaining gold particles, conveying the excavated gold bearing sand andgravel deposits to a discharge point located adjacent the ocean floor,positioning a collection medium at a predetermined distance below thedischarge point, and at a predetermined distance downstream from thedischarge point with respect to the ambient subsurface current adjacentthe ocean floor, discharging the excavated gold bearing sand and gravelmaterial from the discharge point and allowing the material to fall byaction of gravity, the predetermined downstream spacing and thepredetermined vertical spacing between the collection medium and thedischarge point being so related to the magnitude of the ambient oceancurrent adjacent the ocean floor so that the coarse sand and finegravel, and The gold particles will move downwardly and downstream underthe influence of gravity and the ocean ambient current and will bereceived by the collection medium, while the finer sand deposits will becarried downstream beyond the collecting medium, and the heavierparticles will fall upstream from the collection medium.
 2. The processas defined in claim 1 and screening the material received by thecollection medium whereby the smaller gold particles will be separaratedfrom the coarser sand and fine gravel particles.
 3. The process asdefined in claim 1 wherein said gold bearing sand and gravel deposits iscontinuously excavated and is continuously conveyed to the dischargepoint to be continuously discharged therefrom.
 4. Apparatus for underseamining of sand and gravel deposits containing gold particles comprisingan excavating device adapted to be moved along the ocean floor forcontinuously excavating gold bearing sand and gravel deposits, theconveying device having a receiving portion for receiving excavated sandand gravel material, and having a discharge portion, a collection devicehaving an upper portion positioned a predetermined distance below saiddischarge portion of the conveyor device, and being disposed apredetermined distance downstream from the discharge portion of theconveyor device with respect to the subsurface ambient ocean current,the predetermined downstream spacing and the predetermined difference inheight between the collection device and the discharge portion of theconveyor being related to the magnitude of the ambient ocean currentadjacent the ocean floor so that the gold particles and the accompanyingcoarse sand and fine gravel particles will be moved downwardly anddownstream under the influence of gravity and the ambient subsurfaceocean current and received by the collection device, while the finersand particles will be carried downstream beyond the collection device,and the heavier particles will fall upstream from the collection device.5. The apparatus as defined in claim 4 wherein said collection deviceincludes a reciprocating screen at its upper portion and upon which thegold particles and the coarser sand and grain particles fall.